Gianluca,
Yes. Although the official ASKA is better in every way not just treble (I'm not sure I can hear improved quiescent current stability
) The P61 is warmer and more vague sounding that the AKSA - it definitely does have some of the magic though, after all this is where Hugh started from.
If you are worried about the quiescent stability it can be fixed in the same way as 99% of amps do it.
Dave
Yes. Although the official ASKA is better in every way not just treble (I'm not sure I can hear improved quiescent current stability
) The P61 is warmer and more vague sounding that the AKSA - it definitely does have some of the magic though, after all this is where Hugh started from.If you are worried about the quiescent stability it can be fixed in the same way as 99% of amps do it.
Dave
Re: There is nothing simple in really good simple design
Fred,
Would you say that AKSA is better than Peter Daniel-style GC?
After all the ravings about GC, I am wondering if these things really are better than discrete amps? Of course, all amps are different, but what about it?
abo
Fred Dieckmann said:
Fred,
Would you say that AKSA is better than Peter Daniel-style GC?
After all the ravings about GC, I am wondering if these things really are better than discrete amps? Of course, all amps are different, but what about it?
abo
I'm very pleased with my AKSA 100N--Hugh really did a great job on these amps. Unfortunately I can't comment on the P3A.
I heard the Orions 2 weeks ago and was extremely impressed, to the point that I'm toying with building a pair. I'm not sure what layout you're using, but be aware that the AKSA 100W isn't fond of loads under about 3.6 ohms. The two Peerless XLS drivers in parallel dip as low as 2.5 ohms, which Hugh says isn't a great idea.
If the bass doesn't drop too low then you're fine, otherwise I'd consider making 8 channels of AKSA 55W. I believe Hugh also offers a version with 25W that's supposed to be particularly good on tweaters.
Hope that helps!
Dayne
I heard the Orions 2 weeks ago and was extremely impressed, to the point that I'm toying with building a pair. I'm not sure what layout you're using, but be aware that the AKSA 100W isn't fond of loads under about 3.6 ohms. The two Peerless XLS drivers in parallel dip as low as 2.5 ohms, which Hugh says isn't a great idea.
If the bass doesn't drop too low then you're fine, otherwise I'd consider making 8 channels of AKSA 55W. I believe Hugh also offers a version with 25W that's supposed to be particularly good on tweaters.
Hope that helps!
Dayne
I don't want this to become a plug for the AKSA; not what the forum is about. But objective discussion should be no issue, I believe.
The AKSA 55W has been compared to the Gainclones, though of course, in deference to Peter, there is not yet a 'standard' product, though it's clearly moving in that direction. The outcome has been extremely positive for both amps, though in fairness with differences in power rating we are not always comparing apples and apples.
To comment on Dayneger's post, the 55W doesn't like loads below 3.5 ohms; the 100W is happy down to 2.5 ohms.
Fred, thank you for your comments. I think you are on the money; the AKSA is a simple, classic design properly refined and configured. Nough said.
Cheers,
Hugh
The AKSA 55W has been compared to the Gainclones, though of course, in deference to Peter, there is not yet a 'standard' product, though it's clearly moving in that direction. The outcome has been extremely positive for both amps, though in fairness with differences in power rating we are not always comparing apples and apples.
To comment on Dayneger's post, the 55W doesn't like loads below 3.5 ohms; the 100W is happy down to 2.5 ohms.
Fred, thank you for your comments. I think you are on the money; the AKSA is a simple, classic design properly refined and configured. Nough said.
Cheers,
Hugh
Re: Re: There is nothing simple in really good simple design
I have tried the lm3875 chip and have built a few ss amps in the past (citation 12 for example).
the lm3875 is a fine chip. but there is nothing special about it - or it is as good as anything else I have heard, to put it more positively. it clearly lacks in the power department if you want to hear loud music. What it does is that since it is so simple, it allows the builders to focus on the non-electronic part of the construction, aka the Egyptian maple box,.
with a discrete design, you have more freedom (but also more chances to screw up the construction), with topology, components and values, etc. it can be daunting for a beginner, specially someone without a lot of hands on experience or a big check book.
Soundwise, I would not put the lm3875 at top of my chart.
ABO said:
I have tried the lm3875 chip and have built a few ss amps in the past (citation 12 for example).
the lm3875 is a fine chip. but there is nothing special about it - or it is as good as anything else I have heard, to put it more positively. it clearly lacks in the power department if you want to hear loud music. What it does is that since it is so simple, it allows the builders to focus on the non-electronic part of the construction, aka the Egyptian maple box,
.with a discrete design, you have more freedom (but also more chances to screw up the construction), with topology, components and values, etc. it can be daunting for a beginner, specially someone without a lot of hands on experience or a big check book.
Soundwise, I would not put the lm3875 at top of my chart.
P61 at work
Hi Dave,
after the first day of trial-and-listen sessions, here my comments on P61 (ref amp Rotel 960, speakers Dynaudio Contour 25):
- As expected, the bias stability was less than perfect, and I was forced to modify the circuit (using a classic vbe multiplier). Now is stable.
- Low frequencies are somehow weaks, not so extended, and slower than usual
- Mid frequencies are in good evidence and sufficiently transparent
- High frequencies are very bad, opaque, metallic and not refined
I've used the original Rod's info to build the amp and the psu. I'm a little disappointed, I think I'm going to run a spice simulation to verify the theorical schematic. Is that matching your experience?
Regards,
Gianluca
Hi Dave,
after the first day of trial-and-listen sessions, here my comments on P61 (ref amp Rotel 960, speakers Dynaudio Contour 25):
- As expected, the bias stability was less than perfect, and I was forced to modify the circuit (using a classic vbe multiplier). Now is stable.
- Low frequencies are somehow weaks, not so extended, and slower than usual
- Mid frequencies are in good evidence and sufficiently transparent
- High frequencies are very bad, opaque, metallic and not refined
I've used the original Rod's info to build the amp and the psu. I'm a little disappointed, I think I'm going to run a spice simulation to verify the theorical schematic. Is that matching your experience?
Regards,
Gianluca
Gianluca,
Enhance the quality of the P61 this way:
1. Place a quality 1uF film/foil across the Vbe multiplier
2. Set bias to 55mV across the two output device emitters after half an hour of idling with no signal. Correct as necessary.
3. Reduce C5 to 36pF.
4. Insert 15pF silver mica from base of T2 (feedback transistor on diff pair) to base of upper (15030) driver.
5. Increase bootstrap cap to 220uF 35VW, using the best quality electro you can find.
That should do it. Then tell us the result!
Cheers,
Hugh
Enhance the quality of the P61 this way:
1. Place a quality 1uF film/foil across the Vbe multiplier
2. Set bias to 55mV across the two output device emitters after half an hour of idling with no signal. Correct as necessary.
3. Reduce C5 to 36pF.
4. Insert 15pF silver mica from base of T2 (feedback transistor on diff pair) to base of upper (15030) driver.
5. Increase bootstrap cap to 220uF 35VW, using the best quality electro you can find.
That should do it. Then tell us the result!
Cheers,
Hugh
P61 enhanced
Hugh,
first of all thanks for the time you are spending with me and my P61. I'm impress, and I sincerely appreciate your attitude and your help.
I worked quite a few hours on your suggestions, here my comments:
> 1. Place a quality 1uF film/foil across the Vbe multiplier
Done, bias is now even more stable. On a side note, I'm
using a BD139, is that OK? It's strictly necessary to place it on
the heatsink?
> 2. Set bias to 55mV across the two output device emitters after
> half an hour of idling with no signal. Correct as necessary.
Done.
> 3. Reduce C5 to 36pF.
Done (actually I'm using 33pF).
> 4. Insert 15pF silver mica from base of T2 (feedback transistor
> on diff pair) to base of upper (15030) driver.
Done (actually I have R10, R12 100 ohm resistors in series
with the driver's base, correct?)
> 5. Increase bootstrap cap to 220uF 35VW, using the best
> quality electro you can find.
Done (solen non polar).
I also changed the input capacitor C1 to 470nF (over-dimensioned?), and the feedback capacitor C2 to 33uF (low frequency was a little weak in my first test). And now my impressions:
The P61 has totally changed skin. Bass are now well controlled and natural, the midrange is cristal clear, no fatigue at all, and the treble are finally soft, warm, but also very detailed. Listening is now a real pleasure, and I modified the amp back and forth twice (I was a little skeptical, I admit) to check my acoustical sanity.
Is the current AKSA55 that far from my "enhanced P61"?
Anyhow, thanks very much for your suggestions. Now I'm going to another listening session, but I'll be back soon on the forum...
Bests,
Gianluca
Hugh,
first of all thanks for the time you are spending with me and my P61. I'm impress, and I sincerely appreciate your attitude and your help.
I worked quite a few hours on your suggestions, here my comments:
> 1. Place a quality 1uF film/foil across the Vbe multiplier
Done, bias is now even more stable. On a side note, I'm
using a BD139, is that OK? It's strictly necessary to place it on
the heatsink?
> 2. Set bias to 55mV across the two output device emitters after
> half an hour of idling with no signal. Correct as necessary.
Done.
> 3. Reduce C5 to 36pF.
Done (actually I'm using 33pF).
> 4. Insert 15pF silver mica from base of T2 (feedback transistor
> on diff pair) to base of upper (15030) driver.
Done (actually I have R10, R12 100 ohm resistors in series
with the driver's base, correct?)
> 5. Increase bootstrap cap to 220uF 35VW, using the best
> quality electro you can find.
Done (solen non polar).
I also changed the input capacitor C1 to 470nF (over-dimensioned?), and the feedback capacitor C2 to 33uF (low frequency was a little weak in my first test). And now my impressions:
The P61 has totally changed skin. Bass are now well controlled and natural, the midrange is cristal clear, no fatigue at all, and the treble are finally soft, warm, but also very detailed. Listening is now a real pleasure, and I modified the amp back and forth twice (I was a little skeptical, I admit) to check my acoustical sanity.
Is the current AKSA55 that far from my "enhanced P61"?
Anyhow, thanks very much for your suggestions. Now I'm going to another listening session, but I'll be back soon on the forum...
Bests,
Gianluca
Gianluca,
Thank you for your post.
My pleasure to help. One day you might buy one of my kits!
A BD139 is fine. Collector to base should be around 1K5.
100R base stoppers are also fine.
In all seriousness, it is not in your or my interest to have AKSAs out there underperforming. Kits are sold on word of mouth, so they need to be good. This is a simple, classic circuit, but its performance can be extraordinarily high if great care is taken with component selection, dimensioning and layout.
No, it's not so different; not quite as good as the real thing, but close enough...
Ciao,
Hugh
Thank you for your post.
My pleasure to help. One day you might buy one of my kits!
A BD139 is fine. Collector to base should be around 1K5.
100R base stoppers are also fine.
In all seriousness, it is not in your or my interest to have AKSAs out there underperforming. Kits are sold on word of mouth, so they need to be good. This is a simple, classic circuit, but its performance can be extraordinarily high if great care is taken with component selection, dimensioning and layout.
No, it's not so different; not quite as good as the real thing, but close enough...
Ciao,
Hugh
Re: Re: There is nothing simple in really good simple design
I'm not Fred, but I have listened to Peter's amp and my AKSA 55N with the same speakers, in the same room. "All amps are different" is a nice way to summarize things. Speakers were VMPS RM2 and 626R, and the other amps were Ampzilla monoblocks.
The AudioZone GC didn't do very well with the VMPS, and clipped fairly easily. There just didn't seem to be the grip, even at low volumes. The AKSA did remarkably well compared to the Ampzilla -- very good speed, imaging, detail, but not the same bottom end control as the Ampzilla.
That's NOT the end of the story: the GC was tried on Meadowlark Kestrels. Voila! This combination worked very well. The Ampzillas was good, but not special with the Kestrels. Didn't have time to try my AKSAs on them.
Beautifully built GC v. humble 55W kit amp v. rock solid monoblock: which is "better"?? YMMV! I have tested my AKSA v. amps ranging from Krells (incl. FBP650cx) to Classe (monoblocks even), Accustic Arts, MF and others. It holds its own pretty well. For me, the key advantage is that I can tweak and tune it to my needs. Of course I can do the same with my Krell, but it would be a financially questionable venture.
Oh yes: I've also ventured into GC land, with a TDA7294A amp. Not pure 'GC' in construction, but with short signal paths, and components selected for sound. It offers great price/performance, but won't drive my main system speakers as well as my AKSA. For a smaller setup, with tuning (esp. a buffer after volume control), it's working very well.
ABO said:
I'm not Fred, but I have listened to Peter's amp and my AKSA 55N with the same speakers, in the same room. "All amps are different" is a nice way to summarize things. Speakers were VMPS RM2 and 626R, and the other amps were Ampzilla monoblocks.
The AudioZone GC didn't do very well with the VMPS, and clipped fairly easily. There just didn't seem to be the grip, even at low volumes. The AKSA did remarkably well compared to the Ampzilla -- very good speed, imaging, detail, but not the same bottom end control as the Ampzilla.
That's NOT the end of the story: the GC was tried on Meadowlark Kestrels. Voila! This combination worked very well. The Ampzillas was good, but not special with the Kestrels. Didn't have time to try my AKSAs on them.
Beautifully built GC v. humble 55W kit amp v. rock solid monoblock: which is "better"?? YMMV! I have tested my AKSA v. amps ranging from Krells (incl. FBP650cx) to Classe (monoblocks even), Accustic Arts, MF and others. It holds its own pretty well.
For me, the key advantage is that I can tweak and tune it to my needs. Of course I can do the same with my Krell, but it would be a financially questionable venture.Oh yes: I've also ventured into GC land, with a TDA7294A amp. Not pure 'GC' in construction, but with short signal paths, and components selected for sound. It offers great price/performance, but won't drive my main system speakers as well as my AKSA. For a smaller setup, with tuning (esp. a buffer after volume control), it's working very well.
Sonny, frankly speaking - I don't give a damn about "improved circuitry and better components". Does this translate into more desireable sonic caracteristics? If so, more specificly where does the AKSA better the P3A?
As I see it, you're complete right about the AKSA as a complete amp, where highly qualified component selection has been done by the designer. In other words you can be absolutly sure that the circuit has been maxed out component-wise.
But does that nescesseraly translate into AKSA being superior in every aspect? Is it impossible to build a P3A that actually outperfroms the standard AKSA (without Nirvana upgrade)? Have you compared the AKSA and a P3A sonically? And did you remember to some basic critiscism regarding component selection?
I don't doubt that the AKSA is indeed a very competent amplifier. Nor do I doubt that component selection has great influence on the final result. I recognize that the AKSA most surely betters typical P3As built by a reasonable margin.
As I see it, you're complete right about the AKSA as a complete amp, where highly qualified component selection has been done by the designer. In other words you can be absolutly sure that the circuit has been maxed out component-wise.
But does that nescesseraly translate into AKSA being superior in every aspect? Is it impossible to build a P3A that actually outperfroms the standard AKSA (without Nirvana upgrade)? Have you compared the AKSA and a P3A sonically? And did you remember to some basic critiscism regarding component selection?
I don't doubt that the AKSA is indeed a very competent amplifier. Nor do I doubt that component selection has great influence on the final result. I recognize that the AKSA most surely betters typical P3As built by a reasonable margin.
Interesting comment, Sonny. Thank you.
Sobazz, the AKSA uses a similar topology to the P3A. Very similar, but not the same. There are changes to the output stage, the voltage amplifier and the feedback network. These changes, together with very careful layout and meticulous component choice, really do make the difference. Stray capacitance is very important on an audio amplifier because it carries a global feedback loop, as I'm sure you realize. Board design on the AKSAs took literally hundreds of hours, with many prototype pcbs built and discarded.
Human aural perception is extremely discriminating. If the amp is 'voiced' or 'tuned' by ear, or better still, many ears, we will be taking a good engineering solution and progressing it that fundamental next step towards making the amplifier sympatico with the human organism, relaying the medium of music.
Our notion of musicality is critical here. As organic beings, not a single ethnic category of the human race seems to enjoy even minuscule levels of H5, H7, H9 and H11. Yet a poorly designed amplifier will produce almost immeasureable quantities of the higher, odd order harmonics. The essence of good amp design should aim to reduce these harmonics - commonly found in global negative feedback amplifiers - to imperceptible levels. The problem is, levels perceptible to the human ear are almost impossible to measure; even a quality Hewlett Packard 339 Distortion Analyser is struggling to pick up 0.005% of H5 at 10KHz. This corresponds to 86dB down; well within the dynamic range of the human ear, and the evidence would indicate this is subliminally audible, and leads to 'listener fatigue'.
Tube amplifiers have gradual switch on/off curves, and this produces far less artefacts, even in push/pull designs. Bipolar transistors are hugely disadvantaged with their horrific exponential transfer functions. Mosfets have problems of their own, too, as they also switch abruptly and gate capacitance complicates drive. Humans are remarkably capable of perceiving these subtleties; the organic 'feel' of so many tiny aspects of life is remarkably acute. Since music touches the soul, it should come as no surprise that we are fussy about how we perceive it.
The AKSA is almost trivially simple in implementation, but it belies a huge amount of R&D. I deliberately built it without using distortion analysers, and Robert Jones in California measured it only once the whole development cycle was complete. From a measured performance POV it came up smelling like roses. That it is so similar to the P3A topologically is one of life's ironies.
BTW, I hope this is not construed as an attempt to sell the AKSA, to you or anyone else. You asked a question, Sonny gave a slightly cryptic answer, I filled in the gaps. Actually, with some of the highly academic nonsense I've seen on this forum in recent times I'm beginning to ask myself why I spend so much time here!
Cheers,
Hugh
Sobazz, the AKSA uses a similar topology to the P3A. Very similar, but not the same. There are changes to the output stage, the voltage amplifier and the feedback network. These changes, together with very careful layout and meticulous component choice, really do make the difference. Stray capacitance is very important on an audio amplifier because it carries a global feedback loop, as I'm sure you realize. Board design on the AKSAs took literally hundreds of hours, with many prototype pcbs built and discarded.
Human aural perception is extremely discriminating. If the amp is 'voiced' or 'tuned' by ear, or better still, many ears, we will be taking a good engineering solution and progressing it that fundamental next step towards making the amplifier sympatico with the human organism, relaying the medium of music.
Our notion of musicality is critical here. As organic beings, not a single ethnic category of the human race seems to enjoy even minuscule levels of H5, H7, H9 and H11. Yet a poorly designed amplifier will produce almost immeasureable quantities of the higher, odd order harmonics. The essence of good amp design should aim to reduce these harmonics - commonly found in global negative feedback amplifiers - to imperceptible levels. The problem is, levels perceptible to the human ear are almost impossible to measure; even a quality Hewlett Packard 339 Distortion Analyser is struggling to pick up 0.005% of H5 at 10KHz. This corresponds to 86dB down; well within the dynamic range of the human ear, and the evidence would indicate this is subliminally audible, and leads to 'listener fatigue'.
Tube amplifiers have gradual switch on/off curves, and this produces far less artefacts, even in push/pull designs. Bipolar transistors are hugely disadvantaged with their horrific exponential transfer functions. Mosfets have problems of their own, too, as they also switch abruptly and gate capacitance complicates drive. Humans are remarkably capable of perceiving these subtleties; the organic 'feel' of so many tiny aspects of life is remarkably acute. Since music touches the soul, it should come as no surprise that we are fussy about how we perceive it.
The AKSA is almost trivially simple in implementation, but it belies a huge amount of R&D. I deliberately built it without using distortion analysers, and Robert Jones in California measured it only once the whole development cycle was complete. From a measured performance POV it came up smelling like roses. That it is so similar to the P3A topologically is one of life's ironies.
BTW, I hope this is not construed as an attempt to sell the AKSA, to you or anyone else. You asked a question, Sonny gave a slightly cryptic answer, I filled in the gaps. Actually, with some of the highly academic nonsense I've seen on this forum in recent times I'm beginning to ask myself why I spend so much time here!
Cheers,
Hugh
sobazz said:
I recieved those boards saturday and have not have tested them yet, i can only say that from the schematic point of view. It is refined a lot.
As Hugh says, in the output stage .. It is very much the same way i would do it.
Also the feedback path ensures good stability.
Of course a P3A is a good design too. But the last refinement done by hugh does make it a much better design.
He has done a lot of work in ensuring a good stability.
And the circuit uses a 1/4 of the components i do in my amp.
So it is easy to build.
There is many ways of getting the design right the way you wan't ... This makes the circuits so different. I am for current feedback as they work as they work as they work and work... For me the work every time i make them...
Paul Ebert said:
so if I understand it correctly 3 or 4 channels built into each
wooofer cabinet.
What surprises me is a lack of discussion of the power supply
for the said 3/4 channels, and any "rationalisation" possible
here.
For example one big transformer is an option, for 4 channels
seperate rectifiers and smoothing capacitors ?
Using a common supply I'd be tempted to add a little RC
filtering to the mid amplifier and and a little more to the
treble amplifier PS's as the power lost would not be an
issue.
An amplifier with doubled up output devices and the
woofers in parallel should be as good as two seperate
amps ?
Or would they be built as seperate "monoblocks" ?
sreten.
I would not put the amps in the speakers boxes
The vibration will affect the sound ( as it also does to the Xover )
better to put the amps in one big box with the X over aswell or even better have each amp and X-over it their own boxes fairly close to the speakers.
you may be suprised how much having the X-overs close to the amp improves the sound. It is much better that regular bi-wiring.
If you using one tranny this will unavoidably compromise your earthing scheme unless you have a tranny with multiple secondaries...
just a few thoughts
hope it helps
mike
The vibration will affect the sound ( as it also does to the Xover )
better to put the amps in one big box with the X over aswell or even better have each amp and X-over it their own boxes fairly close to the speakers.
you may be suprised how much having the X-overs close to the amp improves the sound. It is much better that regular bi-wiring.
If you using one tranny this will unavoidably compromise your earthing scheme unless you have a tranny with multiple secondaries...
just a few thoughts
hope it helps
mike
Sreten,
Power supplies. Ah, what a question!
An amplifier is a modulated power supply. Consequently the supply must be absolutely clean, no ripple, very low impedance, and completely free from intermodulation between channels. We are making malt whisky here; crystal clean, stream water is essential.
Therefore for any multichannel amplifier, as far as practicable, the power supplies should be independent. The AKSA has two completely independent power supplies, one for left channel, and one for right.
If you are making a five channel system, some economy is possible. You can use one supply for left front and left rear, and another for right front and right rear. The center channel should have a power supply of its own, since speech intelligibility is enhanced if there is absolutely no intermodulation with other channels.
Cheers,
Hugh
Power supplies. Ah, what a question!
An amplifier is a modulated power supply. Consequently the supply must be absolutely clean, no ripple, very low impedance, and completely free from intermodulation between channels. We are making malt whisky here; crystal clean, stream water is essential.
Therefore for any multichannel amplifier, as far as practicable, the power supplies should be independent. The AKSA has two completely independent power supplies, one for left channel, and one for right.
If you are making a five channel system, some economy is possible. You can use one supply for left front and left rear, and another for right front and right rear. The center channel should have a power supply of its own, since speech intelligibility is enhanced if there is absolutely no intermodulation with other channels.
Cheers,
Hugh
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